Watch and Clock Escapements eBook

It may not be amiss to say the arc i is swept
from the center g through the point u,
said point being located ten degrees from the intersection
of the radial a c with the peripheral line a.
It will be noticed that the inner angle of the entrance
pallet A seems to extend inward, beyond the
radial line a j, that is, toward the pallet
center g, and gives the appearance of being
much thicker than the exit pallet A’;
but we will see on examination that the extreme angle
x of the entrance pallet must move on the arc
i and, consequently, cross the peripheral line
a at the point u. If we measure
the impulse faces of the two pallets A A’,
we will find them nearly alike in linear extent.

Mr. Grossmann, in delineating his exit pallet, brings
the extreme angle (shown at 4) down to the
periphery of the escape, as shown in the drawing,
where it extends beyond the intersection of the line
g f with the radial line a 3. The
correct form for the entrance pallet should be to
the dotted line z x y.

[Illustration: Fig. 17]

We have spoken of engaging and disengaging frictions;
we do not know how we can better explain this term
than by illustrating the idea with a grindstone.
Suppose two men are grinding on the same stone; each
has, say, a cold chisel to grind, as shown at Fig.
17, where G represents the grindstone and N
N’ the cold chisels. The grindstone
is supposed to be revolving in the direction of the
arrow. The chisels N and N’
are both being ground, but the chisel N’
is being cut much the more rapidly, as each particle
of grit of the stone as it catches on the steel causes
the chisel to hug the stone and bite in deeper and
deeper; while the chisel shown at N is thrust
away by the action of the grit. Now, friction
of any kind is only a sort of grinding operation, and
the same principles hold good.

THE NECESSITY FOR GOOD INSTRUMENTS.

It is to be hoped the reader who intends to profit
by this treatise has fitted up such a pair of dividers
as those we have described, because it is only with
accurate instruments he can hope to produce drawings
on which any reliance can be placed. The drawing
of a ratchet-tooth lever escapement of eight and one-half
degrees pallet action will now be resumed. In
the drawing at Fig. 18 is shown a complete delineation
of such an escapement with eight and one-half degrees
of pallet action and equidistant locking faces.
It is, of course, understood the escape wheel is to
be drawn ten inches in diameter, and that the degree
arcs shown in Fig. 1 will be used.